Activated lymphocytes are used as a modality of immunotherapy, especially for cancer treatment. Our studies of activated killer cells are in two areas: (A) Effect of aging on cytolytic T lymphocytes (CTL) activity, using a murine model in vitro and in vivo, and (B) Activation of natural killer (NK) cells to produce lymphokine activated killer (LAK) activity, using a human model in vitro. Project (A), CTL and aging: (1) Interleukin (IL)-12 augments the generation of alloantigen-specific CTL through a pathway not independent of the stimulation of interferon-gamma. The effect is dependent upon T cells, and independent of NK cells. IL-12 augments the development of CTL by spleen cells from aged mice in vitro to the level of that generated by spleen cells from young mice in the absence of IL-12. (2) The effect of IL-12 is now being determined in vivo, in tumor-bearing and normal mice of varying ages. A surprising effect on cell populations is being explored. (3) The frequency of phenotypically naive cells (defined as CD44-dim), decreases with advancing age and is accompanied by an increase in the proportion of memory cells (CD44-bright). However, the decreased frequency of naive cells with aging does not fully explain the diminished CTL activity because purified naive cells from aged mice still exhibit an inherently compromised ability to generate CTL compared to those from young mice. (4) Studies are underway to examine alterations in expression of T cell antigen receptor components with aging, and the potential impact on signaling pathways.Project (B), NK and LAK: (1) The specific biosynthetic turnover of the common leukocyte integrin, LFA-1 is more rapid in IL-2 stimulated LAK cells compared to NK cells. (2) Optimal generation of LAK activity is regulated by oxidation-reduction, requiring a reducing microenvironment, and in particular, the synthesis of reduced type glutathione. (3) Studies on the "reverse killing" of MK sensitive "target cells" by IL-2-stimulated but not native NK cells has revealed the involvement of leukocyte integrins. The mechanisms are being explored. (4) IL-12 and IL-2 can synergize in the augmentation of NK activity, and the augmentation is associated with increased transcription of genes encoding for perforin and granzymes. (5) Investigations have begun on signalling pathways initiated by IL-2 and/or IL-12 binding.